Sulfur Dioxide

sulfur dioxide or SO₂, formed when elemental sulfur is burned in air, is a colourless, pungent, choking gas and is the chemical compound most widely used by the winemaker, principally as a preservative and a disinfectant. Sulfur dioxide, as fumes from burning sulfur, has been used since antiquity to preserve and disinfect during the production and storage of foods (see sulfur for more historical detail).

Sulfur dioxide is said to react with oxygen and so prevent wine or juice oxidation. This is an oversimplification because the chemical reaction between sulfur dioxide and oxygen is not rapid so it is not totally effective in preventing chemical oxidation. However, sulfur dioxide reduces oxidation in other ways.